


In Which Alec Lightwood is NOT the Beta He Thought He Was

by greeneyedsourwolf



Category: Shadowhunters (TV), The Mortal Instruments Series - Cassandra Clare
Genre: Alec Lightwood in Heat, Alpha Jace, Alpha Magnus, Alpha/Beta/Omega Dynamics, Anal Fingering, Anal Sex, In Rut, Knotting, M/M, Mating Cycles/In Heat, Omega Alec, Omega Clary, Omegaverse, Plot What Plot/Porn Without Plot, Riding, Rimming, Scenting, alpha Isabelle, ok theres a little plot
Language: English
Status: Completed
Published: 2018-04-14
Updated: 2018-04-14
Packaged: 2019-04-22 23:15:25
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,737
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/14319210
Author URL: https://archiveofourown.org/users/greeneyedsourwolf/pseuds/greeneyedsourwolf
Summary: Alec Lightwood was a beta his entire life. He had no signs of being anything other than a beta and he was okay with that. Until one morning, when he wakes up in Magnus' bed alone and in pain, sweating with his blood boiling and his skin on fire.





	In Which Alec Lightwood is NOT the Beta He Thought He Was

Alec woke up to heat, with burning, itching, uncomfortable  _ fire _ under his skin. It felt like his blood was boiling, and his skin was a bright pink. Every bone in his body hurt, and his muscles ached.

 

He let out a small groan, and open his eyes. Wearily, he pushed himself up and whined as his everything cramped in his body. Was he sick? Had the flu? He  _ never _ got sick. Shadowhunters don’t get sick.

 

He pushed his blankets and sheets off of him. They felt like they were scratching him, despite the fact that Magnus has these soft, silky sheets he usually loved. His skin was _ too _ sensitive, he couldn’t handle it.

 

He stumbled out of bed in search of water, sluggishly walking to the door. He was usually a swift walker, with a natural agility from being a shadowhunter. Today though, he was tempted to lean against the wall as he made his way to the kitchen. He felt weak, and his legs shook with the effort of walking.

 

He could hear voices coming from the kitchen, and he thanked God because he did not feel well. Magnus would know what was wrong, he could always figure out what was happening. And while he was a little embarrassed to be walking into the kitchen sweating and looking like he was about to faint, he needed water and currently, that was the only thing he could think about. 

 

“Jace, why are you being such an alpha today? Get off me,” he could hear Clary challenging her mate with a teasing voice. He hesitated a little, the thought of an alpha other than Magnus in the vicinity of him was almost repulsive. Which was weird, you would not usually shy away from your Parabatai, especially while injured or ill.

 

And Clary, well, he never wanted to be around Clary. There was nothing out of the ordinary there. 

 

“Because you smell especially good today,” Jace answered in a rough tone.

 

He could hear his sister whine, “Ew, Jace, stop. Can’t it wait until after we get the shit from Magnus.” And great, because now there were two alphas and Alec was trying not to panic.  _ Danger _ , his brain supplied. “And Alec’s coming back with us to the institute and I don’t even think he’s up yet.”

 

Coming back to the institute? No. No way in hell. He was really starting to panic now because there was no way he would let two alphas drag him from his warm and safe home, where  _ Magnus _ was, back to the institute where it was not warm and safe and where he would be vulnerable and alone.

 

He slowly made his way to the kitchen, and by the time he got there he was sweating, the fire beneath his skin only increasing in intensity. His eyebrows were drawn together, and a frown plastered on his face as his stomach started to hurt.

 

He walked into the kitchen and immediately to the cupboard, where he shakily grabbed a cup.

 

As he filled it up he heard a gasp, and Isabelle’s soft voice, “Alec…”

 

He didn’t care what she wanted to say. Right now he needed water, and the only thing he could think about was water. That and the fact that his body was heating and burning and glistening with sweat. He turned off the tap and frantically devoured half the glass in one large gulp. He leaned against the fridge, he was starting to feel nauseous.

 

He could hear some shuffling and a few clacking footsteps walking towards him. He recognized those sounds, the heels against the floor, as Isabelle. Isabelle. His sister. An alpha.

 

His eyes shot open and he dropped the half-filled cup in his hand in favor of throwing his arms up in defense. It shattered on the floor, but he barely registered the droplets of water hitting his feet or the loud crash.

 

Everyone’s attention was drawn to him, now. Jace and Clary stared with shocked expressions, his sister’s eyes were wide and confused. 

 

“Alec, you’re… Are you okay?” Isabelle asked quietly. She took a few steps back, giving him some space to calm down.

 

He didn’t say anything, he couldn’t. He didn’t understand. He didn’t understand why he was scared or why he felt like he was going to throw up. He didn’t understand why his body  _ hurt  _ or why the smell of his sister had him practically gagging. But most of all he didn’t understand why they were there and Magnus  _ wasn’t _ . He wanted Magnus, he needed him. Where the fuck was he?!

 

And then Jace was getting up out of his seat, despite Clary’s firm hold on his arm, and he was walking towards him. He shook his head violently, his arms back out and ready to fight. Because he wasn’t safe and all his body was telling him was that is was in danger. Jace stopped, clearly confused. They were Parabatai, and fighting each other was the complete opposite thing people sharing that bond should do.

 

“Dude, it’s just me,” Jace reasoned. Alec just shook his head.

 

Clary, the only omega in the group, spoke up, “Jace, stop. He’s in heat. He doesn’t understand, just back off.”

 

Alec’s got only one word out of that:  _ heat _ . Was he in heat, was that what this was? This burning, itching, grossness inside of him that made him feel sick? No, that was impossible. He was a beta, he _ is _ a beta. He’s 18 for Christ’s sake, and well past the presentation period of his life.

 

Jace took some steps back, returning to Clary’s side. Isabelle did the same. 

 

“Where’s Magnus?” Clary asked. Jace and Isabelle’s eyebrows raised and they looked at her in shock.

 

“You’re not serious? Alec cannot spend a heat with Magnus, that’s ridiculous!” Jace insisted.

 

Alec’s brain immediately caught on to the alpha’s name.  _ His _ alpha, his brain insisted.

 

“What else do you think is gonna happen? Do you suggest we bring him back to the institute? Where he can suffer a terrible, painful first heat alone? And what do you think Maryse is gonna do when we show up with her eldest son heat-ridden and miserable?” 

 

Jace and Isabelle looked at each other. Their parents were going to flip when they find out their son, their eldest, the one meant to take the place of them in their death, is actually an omega and not the beta they thought he was for four years.

 

Jace sighed, “Well isn’t it kind of irresponsible to leave him here with an alpha he’s not even mated to in his first heat?”

 

“Not as irresponsible as it would be to take him away from Magnus!” Clary was starting to get heated. “You have no idea what being in heat is like. And it’s far from irresponsible to leave him with Magnus of all people, the High Warlock of fucking Brooklyn, who is much more capable of taking care of him than we are. Taking him away from the alpha that he practically lives with, the alpha that he’s been dating for almost a YEAR, would be subjecting him to almost  _ unbearable _ pain. And it’s not our decision, it’s his.”

 

She made eye contact with him, and for some reason, he wasn’t nearly as threatened by her as he was the other two. Maybe it was because she was an omega.

 

“Magnus?” She asked, trying to pull an honest response from him.

 

His eyes lit up and he looked around the room because  _ Magnus _ ?  _ Where was Magnus? Was he here? _

 

“And notice that’s the only alpha that doesn’t make him so scared that he looks like he’s gonna puke,” she said. “So, where is he?”

 

“Should be back any minute. He left right after I got here, said he would be back in ten. It’s been twenty, but he’s lucky I’m patient,” Isabelle replied.

 

As if on cue, Magnus walked into the room. He was carrying a small, purple bag, looking amused.

 

He smiled, “I acquired your necessities. I’m sorry for being late, though I do have a good st-” As soon as he looked up he stopped talking. 

 

Alexander was in distress. Alexander was in  _ heat _ .

 

Alec’s entire body lurched forward as he heard the familiar voice, and frantically searching the room for its source. Magnus’ eyes locked on his and it took everything in his being not to whimper at him. His fingers clawed against the fridge behind him, and he leaned forward to take a step, grateful that he was finally here. 

 

What was minutes without Magnus felt like hours.

 

“Alec, stop! The glass!” Isabelle exclaimed.

 

Alec flinched at the sudden loudness and stepped back again. 

 

Magnus handed Isabelle the bag, “Everything’s in there. Get out. All of you.”

 

They practically ran out the door.

 

Magnus heard the door close and he quickly made his way over to Alec.

 

“Magnus,” the younger man breathed. He almost tried to walk towards him again, but the alpha held up a hand to stop.

 

And, okay, he was starting to feel the tell-tale signs of heat. Because first all he felt was pain and thirst, and then he was scared, but now? Now Magnus was in front of him and the only thing he could think about was Magnus being  _ inside _ of him.

 

The warlock snapped his fingers and the glass was gone. Alec looked at the ground for a second, taking a second to process that he can move. Then he sprints to Magnus and hugs him, shoving his nose into the alpha's neck and taking a long, much-needed breath of that spicy, vanilla scent.

 

“You presented very late, Alexander,” is all Magnus says and the omega grabs at him, whining into his neck.

 

Alec nods. “Please,” he says.

 

Magnus is wearing far too many articles of clothing, it’s preventing Magnus from touching him,  _ really _ touching him. Not to mention his owns clothes are scratchy and hot against his skin, taking his already-high temperature and raising it another notch. He starts to pull Magnus’ purple, velvet coat off as he whines to get closer.

 

“Okay, okay,” Magnus reassures him softly. “I’m not going anywhere. Come on, let’s go to the bedroom.”

 

Alec follows his alpha, feeling much better after having scented him. The heat is still there, but it’s not sizzling under his skin like it was before. And for that, he was grateful.

 

He stripped in no time, the alpha following. The coolness of the room hit his skin and he breathed a breath of relief.

 

Magnus pulled him in for a kiss. One hand caressed his cheek, and the other wrapped around his waist, pulling him in. Alec tried to go slow, to be gentle and take his time kissing the alpha. But everything was starting to get foggy again and the fire was lighting in his stomach once more. He deepened the kiss, adding a sense of urgency to the equation. The alpha growled in response.

 

He could feel Magnus’ hardening member press against his leg and he started to whine into the kiss. The omega’s hands roamed all over his body, grabbing his asscheek, pulling him in, one hand dragging nails down the alpha’s chest as he whispered little  _ please _ ’s into his ear.

 

The hand Magnus had wrapped around his back dipped a little lower, fingers trailing over Alec’s crack. Alec was leaking slick, he could tell now. There was an unfamiliar wetness seeping between his cheeks. Alec wasn’t sure how he could get used to this.

 

“Relax,” Magnus said. He kissed down Alec’s neck and under his chin, “I know it’s new, but you’ll get used to it. All omegas do.” 

 

Being called an omega was new in itself, but Alec smiled. He liked it. He could like being called omega, Magnus’s omega,  _ my omega _ . He could get used to that.

 

In fact, he was getting wetter just thinking about it. Magnus could tell, the air was thick with the smell of heat slick. He growled and Alec just whimpered.

 

“Please, alpha.”

 

Magnus growled again, pushing Alec back onto the bed. He took note of the fact that all the blankets and sheets are on the floor. He leaned over Alec, who was now laying on his back, and whispered, “Sheets too much for you? You too sensitive, omega?” And with that, he ran a hand down Alec’s chest and stomach.

 

His fingertips barely brushed Alec’s skin but it was sending livewires down his body. He whined and arched into the touch. He was so wet. He was so ready for Magnus to take him, fuck him good and proper and knot him again and again.

 

“Turn around,” Magnus ordered.

 

He flipped over onto his stomach as fast as he could. Magnus smiled and leaned over him. He started to kiss his neck, and down his spine. The omega tried to stay still as he let out little moans. Magnus’ fingers reached down and started to circle Alec’s hole.

 

They had sex before, sure, but this… this was something else. Getting prepped before was fun, and it felt good, but this felt  _ amazing _ . His hole was so sensitive, each and every of Magnus’ touches was sending shocks straight to his cock. Magnus was still kissing him everywhere: his arms, his shoulders, his hips. He licked and nipped at his neck, making the omega gasp and push back against him.

 

Magnus pushed one finger into the omega’s hole, and it slid in with almost no resistance with how wet he was.

 

He groaned, “More, please, more.” He backed his hips up, and Magnus pushed him back down to the bed with a sigh.

 

“Patience, Alexander.”

 

Magnus added another finger, pushing into Alec’s slick hole slowly. He grinned at the small noises spilling out of the omega and started to scissor him open. Much to Alec’s dismay, the alpha avoided his prostate, letting him suffer as his fingers thrust in and out of him. There wasn’t much more he could do than lay there and take what Magnus offered him.

 

Alec’s hands gripped the sheets beneath him, and he dug his face into the pillow, taking in his alpha’s perfect, mouthwatering scent. He lifted his head up every so often to moan and groan, urging Magnus to just  _ take him already _ . 

 

He started to pick up the pace. It was making Alec squirm and cry out, he was desperate. Magnus hadn’t even touched his cock but it was red and hard and leaking. He wanted to come, he wanted to come  _ so bad _ . The heat was burning inside of him, and he just wanted a little bit of release, a little bit of relief.

 

And then he felt something warm and wet press against his entrance. He gasped, almost jumping out of Magnus’ grip.

 

“What are you-” he looked behind him just at Magnus’ tongue dipped inside. “Oh,  _ Angels _ .” His head dropped back down onto the pillow, and he groaned loudly. 

 

Magnus moaned as well, reveling in the intoxicating scent of his omega’s slick. It was sweet like candy, and it smelled fucking divine. He lapped at it, his tongue swiping mercilessly over Alec’s sensitive hole. The omega could feel the familiar heat of an orgasm growing inside him as Magnus jabbed and licked and sucked.

 

“Please, fuck me. I need it, please  _ please _ ,” he had never felt such an intense need in his life. The feeling of heat under his skin and the burning of his body was nothing compared to how much he wanted Magnus inside of him. He felt so drawn to the alpha, like his entire body was just crying out to him. 

 

Unexpectedly, Magnus slid another finger in and began to thrust into his entrance with deadly precision. He slid past his prostate, holding the omega down by the hips as he arched up and cried out, “Oh yes, oh yes,  _ Please _ .” Alec’s cock was dripping with precome, red and swollen with need as that sweet little bundle of nerves was massaged again and again and again.

 

“You close, baby?” Magnus asked, his voice dripping with lust. He kissed the omega’s thighs, calming his spasming muscles. “Want to come?”

 

Alec let out little pleas, each one more incoherent than the last. Yes, he wanted to come. He wanted to come  _ so bad _ . His body was screaming out for more: more touch, more feel, more Magnus. 

 

The alpha seemed to pick up on his desperation because he speeds up, fingers thrusting in and out of Alec’s hole with an obscene squelching sound. The tips of his fingers swept past his prostate, and Alec let out little whines every time the entered him.

 

The moment Alec’s hand wrapped around his leaking member, the omega was hit with one of the most intense orgasms of his life. He cried out, arching off the bed with a litter of begs and pleads and thanks on his tongue. He moaned little  _ yesyesyes’s  _ as a pool of semen collected on his stomach. 

 

Magnus didn’t let up, adding another finger to the mix. Not that Alec was complaining, his oversensitivity only lasted a minute before the need set in again. With every second he got close to getting what he wanted.

 

“You want my cock, Alexander?” The omega shuddered and moaned, nodding. “Want my knot filling you up?” His fingers fell from Alec’s hole and the omega whined, pushing back against him.

 

Magnus hushed him with a whisper and sat back, “Get on your knees, Omega.”

 

Alec quickly obliged, getting on his hands and knees. He practically presented for Magnus, shoving his ass up in the air and arching his back. He could hear the alpha moan behind him, murmuring appreciation, “So beautiful, Alexander. You are so beautiful.”

 

Alec felt warm hands grip his hips, and the blunt press of his alpha’s cock against his entrance. He moaned, moving his hips back in encouragement. “Patience,” Magnus whispered before pressing in. The tip of his cock dipped into Alec’s entrance with ease, and they both moaned in unison.

 

In took a minute or so until Magnus was fully sheathed inside of Alec. The omega moaned at the fullness of his cock inside of him, it was exactly what his body had been screaming for. Magnus was waiting patiently, a firm grip on his hips in an effort to let Alec adjust to his size.

 

“‘M ready, please Magnus,” Alec moaned into the pillow beneath him, clenching around the swollen cock inside of him. “Fuck me.” 

 

Magnus growled, pulling out slowly until only the head of his cock was inside, and then ramming back in with an intensity that had Alec gripping the sheets and screaming out, “ANGELS!” He practically ripped the velvet sheets that were gripped in his hand.

 

Magnus brought a sense of ferociousness to the bedroom that he hadn’t before Alec presented as an omega. A brutal rhythm was set, each thrust accompanied by a groan. Alec tried to push back, to help, but Magnus held his hips still and fucked into him with a growl.

 

Magnus’ loft would probably smell like heat for weeks, but he didn’t care. He liked it, the smell of his omega, his  _ mate _ , lingering in the air only made his inner alpha purr with possession. Anyone and everyone would know Alec was  _ his _ , and only his.

 

“So good,” the alpha growled. “You feel so good, omega.”

 

Alec was bucking and moaning, his senses enveloped in the smell of heat and slick and alpha and - rut? He looked over his shoulder, eyeing Magnus in curiosity. His eyebrows were furrowed, eyed closed, the look of pleasure and concentration ever-present on his face. When he opened his eyes they were red, not the gold they usually were.

 

“You’re - ah, ah  _ fuck _ \- y-you’re in rut,” he hiccuped as the alpha filled him again and again.

 

“Your heat triggered it,” he replied with a grunt. 

 

Alec had only spent one rut with him before, a couple of months ago. He remembered liking the smell of Magnus, the roughness, and the praises he would receive from the desperate alpha. Now, the smell was overwhelming, and it only brought the omega closer to the edge.

 

“Oh there, _ there _ ,” Alec pleaded, his voice cracking as the Magnus’ cock created a delicious friction against his prostate. He own member was trapped, hard and leaking, against the sheets. He was  _ so _ close.

 

He could sense Magnus was as close as he was, as his hips started to falter with each thrust. Their groans became louder, Alec whimpered and whined as Magnus’ knot slowly swelled inside of him.

 

“Please, alpha. Knot me, I need you so much, please!” Alec reached for his cock, but Magnus smacked his hand away and grabbed it himself. He jacked him off to the same rhythm as his thrusts. Alec’s legs and arms were shaking, he could barely hold himself up with the feel of the knot growing and grinding inside of him. 

 

Magnus let go of his hip and reached under him to pull him back against his chest. They were now chest-to-back, and Alec was practically sitting in his lap as Magnus made a few hard, final thrusts into his wet heat.

 

With a groan, Magnus’ knot popped. Alec practically screamed as he came, clenching down on the hard member inside of him as he trembled through one of the most intense orgasms of his life. His head fell back onto Magnus’ shoulder, whimpering as the alpha ground his knot against the sensitive bundle of nerves inside of him.

 

Magnus carefully moved them and layed down, wrapping his arms around Alec with a sigh. The haze of lust was clearing, and they were both becoming more coherent by the minute. Alec was purring softly, which was surprising to Magnus considering he had never done that when he thought he was a beta.

 

“Better?” Magnus asked softly, petting his precious Alexander’s hair.

 

Alec nodded, “So much better.”

 

“You’re an omega.”

 

“I’m just as surprised as you are,” Alec said, his voice raw. “My mother’s gonna kill me.”

 

Magnus chuckled and pulled the omega close to him. They would have to wait forty or so minutes until his knot went down, and then Magnus planned for a shower and round two, and maybe even some food.

 

“You smell good,” Magnus whispered into his ear.

 

“Mhmm, you too,” Alec replied, drifting off into sleep.

**Author's Note:**

> Hoped you guys liked it, it turned out being like a thousand words more than I expected but whatever.


End file.
